Cisco 400-007 Exam With Confidence Using Practice Dumps

In a standard 3-tier data center architecture (access, aggregation, core), the Layer 2-to-Layer 3 boundary typically resides at the aggregation layer. When extending VLANs between data centers using a Layer 2 interconnection, the most optimal and scalable termination point is at the aggregation layer because:

It naturally handles VLAN demarcation and Layer 3 boundary.

Spanning Tree Protocol (STP) domains remain contained within local aggregation blocks.

The core remains Layer 3-only, ensuring scalability, stability, and no STP involvement.

Simplifies traffic engineering, FHRP operations, and minimizes control-plane complexity across sites.

This design is consistent with CCDE v3.1 best practice where VLAN extension is isolated to aggregation to avoid STP scaling issues and maintain hierarchical design principles.

Why other options are incorrect:

A: STP isolation can still be achieved at aggregation while keeping the core Layer 3.

C: Access layer extensions would increase STP scope and complexity unnecessarily.

D: Core termination violates Layer 3 core design, bringing STP into the core, which is not scalable.

C (Transparent firewall): Operates at Layer 2, allowing filtering and inspection of traffic within the same subnet without requiring IP routing changes. It performs deep packet inspection while maintaining Layer 2 adjacency, making it ideal for intra-subnet traffic control in data centers.

This allows security segmentation inside broadcast domains, enforcing security policies even for east-west traffic.

Other options explained:

A: Routed firewalls require subnet boundaries and are not ideal for intra-subnet control.

B: VLAN ACLs provide basic filtering but lack deep packet inspection capabilities.

D: Zone-based firewalls are primarily designed for inter-subnet (Layer 3) traffic segmentation.

A: The overload bit (OL bit) signals other routers to avoid using the overloaded router as a transit path for Level 2 traffic. However, the overloaded router can still forward Level 1 local area traffic if applicable.

D: The overload bit is commonly used during router bootup to prevent temporary black holes while the router completes its routing protocol convergence and LSDB synchronization.

Why other options are incorrect:

B: CSNP prioritization is not related to overload bit functionality.

C: LSDB synchronization occurs through normal IS-IS mechanisms; overload bit is not involved.

E: The overload bit prevents transit usage, not attracts traffic.